India’s Polar Satellite Launch Vehicle, in its thirty-seventh flight (PSLV-C35), will launch the 377 kg SCATSAT-1 for ocean and weather related studies and seven co-passenger satellites into polar Sun Synchronous Orbit (SSO). Co-passenger satellites are from Algeria, Canada and USA as well as two satellites from Indian Universities/ Academic Institute.

SCATSAT-1 will be placed into a 720 km Polar SSO whereas; the two Universities/ Academic Institute Satellites and the five foreign satellites will be placed into a 670 km polar orbit. This is the first mission of PSLV in which it will be launching its payloads into two different orbits.

PSLV-C35 will be launched from the First Launch Pad (FLP) of Satish Dhawan Space Centre (SDSC) SHAR, Sriharikota. It will be the fifteenth flight of PSLV in ‘XL’ configuration (with the use of solid strap-on motors).

The PSLV-C35 is scheduled to be launched on Monday morning at 9:12 hrs (IST) on September 26, 2016 from SDSC SHAR , Sriharikota.

But, I m completely surprised and cannot make out why an XL is used. The weight of satellites is almost equal to the last CA version launch for Singaporean satellites.

A CA should be enough for the weight - but i think this time a dual launch structure is also flown, so we have a greater launch mass than in the Singaporean mission, which might push it over the CA limit.

But, I m completely surprised and cannot make out why an XL is used. The weight of satellites is almost equal to the last CA version launch for Singaporean satellites.

A CA should be enough for the weight - but i think this time a dual launch structure is also flown, so we have a greater launch mass than in the Singaporean mission, which might push it over the CA limit.

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Currently, two versions of PSLV are operational, namely PSLV-XL (with six extended version of Strap-on motors) and the PSLV Core-alone (without Strap-on motors).

But, I m completely surprised and cannot make out why an XL is used. The weight of satellites is almost equal to the last CA version launch for Singaporean satellites.

A CA should be enough for the weight - but i think this time a dual launch structure is also flown, so we have a greater launch mass than in the Singaporean mission, which might push it over the CA limit.

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Currently, two versions of PSLV are operational, namely PSLV-XL (with six extended version of Strap-on motors) and the PSLV Core-alone (without Strap-on motors).

On September 26, the PSLV satellite launcher will for the first time place its multiple passengers in two different orbits.The flight is also significant as it will last two hours and 15 minutes, making it the PSLV’s longest ever.

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Only the main passenger, ISRO’s 370-kg Scatsat-1 ocean and weather tracker, will get off first at a slightly higher orbit at 720 km. It will be out in the first 17 minutes, as is customary.The remaining smaller satellites, weighing between 5 kg and 110 kg, will be ejected at 670 km — but after about two hours.To make this possible, launch team engineers will shut down and restart the fourth and last stage of the vehicle (called PS4) twice during the flight, according to two senior officials in the know.

MUMBAI: It promises to be a historical Indian space mission for three reasons on September 26. It will be the first time that a satellite, Pratham, designed and developed by the students of IIT-Bombay will be launched. Second, only 18 days after successfully launching a weather satellite, Insat-3DR, another one, ScatSat-1, will be placed in orbit for the first time.

Third, in its 23-year-old history, it will be the first time that the highly proven four-stage PSLV will be launching satellites into two different orbits. For Monday's flight the launcher will be the advanced version of the PSLV called the PSLV-XL.

According to Isro, while the main satellite, ScatSat-1, will be placed into a 720-km polar sun synchronous orbit, the remaining ones will go into a 670-km polar sun synchronous orbit. For this complex manoeuvre, Isro had earlier carried out a test of successfully shutting down and restarting the fourth stage engine of the PSLV.

This is the first mission of PSLV in which it will be launching its payloads into two different orbits.

The multiple burn technology was first tested by ISRO while flying its PSLV rocket on December 16, 2015.

Launching of multiple satellites with a single rocket is nothing new for ISRO and it has been doing that for several years. The challenge, however, is to launch several satellites at different orbits with one rocket.

"Restarting a rocket engine soon after it is shut off is a critical technology that has to be mastered. Once a rocket engine is activated, then the heat generated is very high. The trick is to cool it down in the space and to restart it at a short gap," an industry expert had told IANS.

"This is entirely different from switching on and off the communication satellite's engines in the space. The interval between two restarts of a communication satellite engine will be in days. But in the case of restarting a rocket engine, the time gap will be in hours," the expert added.

"By that time the rocket's engine has to be cooled down. This part of the experiment is very critical," he explained.[/b]

According to this Deccan Chronicle Report, the fourth stage will be cut off after 17 minutes of flight, then it will be restarted twice.

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Satish Dhawan Space Centre director P. Kunhi Krishnan said the ScatSat-1 will be separated within 17 minutes of launch, after the fourth stage is shut off. The stage will be ignited briefly after 1 hour and 22 minutes and stopped. It will be started again about 40 minutes later, and the last satellite will be placed in orbit about 2 hours and 15 minutes after launch.

This multiple rocket engine burn technology was tested in two PSLV Missions before.

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"We have demonstrated the fourth stage engine restart capability. The fourth stage was restarted once in case of PSLV C-29 and twice with respect to PSLV-C34", Mr Kunhi Krishnan told this newspaper.

Although cost saving is less, this approach would save few strap-ons for follow on launches. It has some positive impact on the frequency of the launches, which is current limited by manufacturing capacity limits